The Hidden Digidesign Pro Tools (part 3)

This is where we really get to the fun stuff. Heres an old problem: a guy comes in with an acoustic guitar and strums a backing for a song. Fine. Then he says that he wants to add a MIDI drum track...

By
David Mellor

Thursday January 1, 2004

Tempo Mapping

This is where we really get to the fun stuff. Heres an old problem: a
guy comes in with an acoustic guitar and strums a backing for a song. Fine.
Then he says that he wants to add a MIDI drum track. Politely you suggest that
he should have done it the other way round, or at least strummed to a click,
because it is far easier to add acoustic guitar to a MIDI track than to do it
the other way round and maintain some sort of rhythmic correspondence between
the two. But why should the paying customer have to compromise because of these
technicalities, and he might anyway want to preserve the rhythmic ebb and flow
of his original acoustic meanderings. Panic not, Pro Tools can help, and heres
how...

First, record the free-tempo track into Pro Tools, preferably with a clear
count in. Once the recording is made, punched into, edited and whatever else
it takes to achieve perfection, edit out the section before the count in and
bring the rest forward in time so that it starts exactly at the beginning of
the timeline. This helps everything else make sense. Now position the cursor
on the first count and from the Edit menu select Identify Beat.
This allows you to specify the current position of the cursor in terms of bars
and beats, i.e. bar 1 beat 1, and also a meter setting can be entered. When
you have done this a small triangular beat marker will appear in the timeline.
Reposition the cursor so that it sits exactly on the first beat of the second
bar, repeat the process and specify that this is bar 2, beat 1. By the time
you do this for the third bar, Pro Tools will have anticipated the basic tempo
of the track and will probably guess accurately what bar and beat you want this
to be. Continue throughout the track to the end. Obviously this will take a
little time, but at the end of the process what you have is a Tempo Map and
any MIDI recorded into the session can be quantised according to this tempo
map and be in perfect time with the original free tempo audio. You have to hear
it to believe how well this can work. If the tempo varies widely then you might
find that a little additional work is required. The triangular beat markers
can be grabbed and slid along the timeline to make small adjustments. If the
tempo varies significantly within a bar then additional markers can be added.
Funnily enough the Pro Tools manual advises not to bother with all of this and
record to a click in the first place. How boring.